There is some argument about calculating distances from the GPS receiver and the 3 satellites. The solution to this is the satellites send a time stamp with their signal. Consequently the only atomic clocks required are on board the satellites themselves and not on every receiver. At that the satellites need only be updated by an atomic clock. This is how distances are calculated. Once they're determined, the GPS coordinates can be found with just the coordinates of the satellites. This web page I made shows how.